non-union states have lower SAT scores

Only five states do not currently allow collective bargaining for educators. Those states and their SAT/ACT rankings are as follows:
South Carolina: 50
North Carolina: 49
Georgia: 48
Texas: 47
Virginia: 44

I’ve seen it in a gazillion places, do not know the source.

Critique: Correlation ≠ causation. We can conclude neither that low test scores lead to no collective bargaining, nor that the lack of collective bargaining leads to low test scores. We can say safely that there appears to be some sort of link.